IEEE1588 has been proposed as a technique for synchronizing time of devices on a network in the precision less than a microsecond. A synchronization method by the IEEE1588 is realized by a grand master mode device, a boundary clock mode device, and an ordinary clock mode device, for example. The grand master mode device is directly connected to an accurate time source, such as a global positioning system (GPS) satellite, a standard wave, and an atomic clock. The boundary clock mode device relays time information which is transmitted from the grand master mode device. The ordinary clock mode device terminates the time information which is transmitted from the grand master mode device.
The grand master mode device receives time of day (TOD) and a pulse per second (PPS) from an accurate time source such as a GPS satellite so as to synchronize time thereof. On the other hand, the boundary clock mode device and the ordinary clock mode device transmit a PTP packet for inquiring time to the grand master mode device by using the precision time protocol (PTP) at arbitrary timing.
The grand master mode device receives the PTP packet for inquiry. The grand master mode device transmits a PTP packet for time notification including TOD and a PPS to the boundary clock mode device and the ordinary clock mode device, after time-stamping transmission time of the PTP packet for time notification.
The boundary clock mode device and the ordinary clock mode device calculate delay time on a transmission channel by using the timestamp on the transmission of the PTP packet for inquiry and the timestamp of the PTP packet for time notification. The boundary clock mode device and the ordinary clock mode device perform time-correction with respect to time of the PTP packet for time notification which is transmitted from the grand master mode device, so as to synchronize time thereof.
“IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems” IEEE Std 1588-2008 is an example of related art.